The present invention relates to novel catalyst structures prepared with use of glass fiber products.
Granular catalysts 5 to 10 mm in size have been generally used for vapor-phase catalytic reaction systems. Such catalysts have been found empirically favorable with respect to minimizing pressure loss of the reactant gas in the catalyst layer and minimizing clogging of the catalyst layer and further from the viewpoint of economy. On the other hand, however, such granular catalysts do not permit gaseous reactants to diffuse into the catalyst effectively, that is, fail to permit a high rate of mass transfer. A great difference therefore occurs in the reactant concentration within the grains or pellets, with the result that the catalyst is low in the effectiveness factor defined by Thiele et al. Thus there is the likelihood that almost all the charge of catalyst is unable to function substantially effectively. The low catalyst effectiveness factor poses a serious problem with expensive noble metal catalysts and is very unfavorable economically even in the case of relatively inexpensive catalysts of metallic oxides in respect of the pressure loss of reactant gases, the size of the reactor, the selectivity of reaction, etc.
Generally catalysts for use in industries must fulfill the following requirements:
(1) High activity per unit weight of the catalyst. PA0 (2) High activity per unit volume of the reactor. PA0 (3) Small pressure loss of the reactant gases in the catalyst layer. PA0 (4) High overall strength enabling the catalyst to fully withstand the impact of charging. PA0 (5) High surface strength against the external forces to be exerted on the catalyst during use. PA0 (6) Reduced variations in activity despite the lapse of time. PA0 (7) Low cost.
The true activity of a catalyst, free from mass transfer resistance, per unit weight thereof is dependent on the composition of the catalyst, the structure of the crystals thereof, etc. and is inherent in the catalyst, but the actual activity varies with the grain size, the pore structure of the grain, the flow rate, i.e. linear velocity, of the reactant gas, etc. Generally the activity increases with decreasing grain size, increasing pore size, increasing pore volume and increasing flow rate of the reactant gas. Nevertheless, these factors contributing to the increase of activity are entirely in conflict with the requirments in respect of the reactant gas pressure loss and catalyst strength. Accordingly it is extremely difficult to fulfill all the foregoing requirements (1) to (7).
In order to satisfy the above requirements (1) to (7), several catalysts of the honeycomb type have been developed in recent years. These catalysts include those prepared by forming a paste from a catalytic component and a binder, extruding the paste into a honeycomb body and baking the body under suitable conditions, and those prepared by making a honeycomb structure from ceramics having no catalytic activity and depositing a catalytic component on the surface of the structure with a binder. With the former catalysts, there is the need to form a honeycomb body with a large wall thickness and to obtain a compacted baked body which is less amenable to the diffusion of reactant gases into the catalyst, in order to give the desired strength to the catalyst. It is therefore impossible to afford an improved catalyst effectiveness factor. Thus difficulties are encountered in improving both strength and activity at the same time. With the latter case, the tough ceramics honeycomb structure has ideal overall strength, fulfilling the requirement (4), but the use of the binder reduces the inherent activity of the catalyst. Further the layer of deposited catalytic component, which is made very thin to assure high surface strength (5) and high activity per unit weight (1), reduces the activity per unit volume of the reactor (2) and impairs the stability of reaction.